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What is the proton-proton cycle in the Sun?

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laser-activated fusion — nuclear fusion Interior of the U.S. Department of Energy's National Ignition Facility (NIF), located at Lawrence Livermore National Laboratory, Livermore, California. The NIF target chamber uses a high-energy laser to heat fusion fuel to temperatures sufficient for thermonuclear ignition. The facility is used for basic science, fusion energy research, and nuclear weapons testing.

The proton-proton chain is a series of thermonuclear reactions that serves as the primary energy source for the Sun and other cool main-sequence stars. In this process, four hydrogen nuclei (protons) are fused to form one helium nucleus.12

The reaction proceeds through several steps:
* Two hydrogen nuclei combine to form a deuterium nucleus, emitting a positron and a neutrino.12
* The deuterium nucleus captures another proton to form a helium-3 nucleus, releasing a gamma ray.12
* Ultimately, these reactions result in the formation of a helium-4 nucleus.12

Because approximately 0.7 percent of the original mass is converted into energy during this fusion, the process releases significant heat and radiation. This energy generation is essential for the Sun's stability and luminosity, allowing it to radiate energy over billions of years.12